For the protection of articles, in particular of clothing, from theft in retail stores, it is known to fix an antitheft device to each article. If a person attempts to take the clothing article away fraudulently, the antitheft device influences a detector placed in an alarm gate installed at the store's exit. To avoid the alarm going off when an honest customer leaves the store, there are several processes according to the type of influence means housed in the device.
If the antitheft device is designed in the form of a badge, the store staff must remove the device before the customer passes through the alarm gate. The retailer must therefore have a stock of badges, attach the badges before putting them on sale, and remove the badges each time a sale is made. This is very restricting.
According to DE-A-32 12 039, an antitheft influence device is known, being presented in the form of a thin label with an oscillating coil circuit, which can be used to equip numerous articles, books, clothing articles, etc. To neutralize the label, the document proposes cutting or punching or piercing part of the label in order to destroy the electrical conductors.
When the thin oscillating circuit label is not accessible for direct destruction, its neutralization will prove impossible to carry out.
Document CH-A-656 472 describes an antitheft label comprising a pre-cut portion. To neutralize the label, the pre-cut portion is removed, this portion containing part of the circuit forming the coil. In practice, this label did not give satisfaction as dishonest customers can easily understand, from the presence of the pre-cut dotted lines, the method used to neutralize the label, and can therefore use this method themselves before going through the alarm gate.
Document EP-A-0 209 916 discloses a process for neutralizing the same thin oscillating circuits. The coil is placed in a magnetic field sufficiently intense to allow the induced current flowing in the coil to trip a neutralization device provided.
The drawback of this process is that the neutralization proves to be reversible, thus leading to the reactivation of the thin antitheft label, in particular as a result of temperature or mechanical stresses.
According to document EP-A-0 123 557, an antitheft influence means is known, presented in the form of a fine thin band of ferromagnetic material. The neutralization of this ferromagnetic marker is made possible by attaching to the band small sections which can be magnetized. When a magnetic field is applied, the small sections are magnetized and permanently polarize the ferromagnetic band. The marker becomes undetectable to the monitoring device.
This neutralization also has the drawback of being reversible as the magnetization of the small sections in question can decrease in intensity over time and thus allow the ferromagnetic band's activity to reappear.
According to document FR-B-2 623 003, a magnetic marker is also known which can be deactivated by subjecting it to an amplitude and/or frequency field much higher than the amplitude or frequency of the detection field. The effect of this deactivation is to dislocate the borders of the magnetic domains of the marker, which then has a hysteretic characteristic different from that in the active state. This method of neutralization can however be of a reversible nature and, in any event, only relates to magnetic markers having a hysteretic characteristic already established when the marker is designed.
The purpose of the invention is to overcome these drawbacks of a lack of efficiency in known magnetic and mechanical neutralization systems.